Pigments are a class of colorants useful in a variety of applications such as, for example, paints, plastics and inks, including inkjet printing inks. Dyes have typically been the colorants of choice for inkjet printing inks because they are readily soluble colorants which enable jetting of the ink. Dyes have also offered superior and brilliant color quality with an expansive color gamut for inks, when compared to conventional pigments. However, since dyes are molecularly dissolved in the ink vehicle, they are often susceptible to unwanted interactions that lead to poor ink performance, for example photooxidation from light (will lead to poor lightfastness), dye diffusion from the ink into paper or other substrates (will lead to poor image quality and showthrough), and the ability for the dye to leach into another solvent that makes contact with the image (will lead to poor water-/solvent-fastness). In certain situations, pigments are the better alternative as colorants for inkjet printing inks since they are insoluble, have higher chemical and thermal stability compared to dyes, and since they are not molecularly dissolved within the ink matrix but rather dispersed as fine particles in the ink, do not generally experience colorant diffusion. Pigments can also be significantly less expensive than dyes, and so are increasingly attractive colorants for inkjet printing inks.
Key challenges with using pigments for inkjet inks are their large particle sizes and wide particle size distribution, the combination of which can pose critical problems with reliable jetting of the ink (i.e. inkjet nozzles are easily blocked). Pigments are rarely obtained in the form of single crystal particles, but rather as large aggregates of crystals and with wide distribution of aggregate sizes. The color characteristics of the pigment aggregate can vary widely depending on the aggregate size and crystal morphology. Thus, an ideal colorant that is widely applicable in, for example, inkjet inks and toners, is one that possesses the best properties of both dyes and pigments, namely: 1) superior coloristic properties (large color gamut, brilliance, hues, vivid color); 2) color stability and durability (thermal, light, chemical and air-stable colorants); 3) minimal or no colorant migration; 4) processable colorants (easy to disperse and stabilize in a matrix); and 5) inexpensive material cost.
The following documents provide background information:
U.S. Pat. No. 7,008,977 discloses colored fine resin particles having a structure in which a conventional, sub-micron sized pigment particles with diameters of about 500 nm, which are coated with a water-insoluble resin is encapsulated with a copolymer composed of at least a polymerizable unsaturated monomer and reactive emulsifier. Examples provided in the invention provided use dry commercial pigments that were pre-processed with resinous surface additives to aid dispersability in a monomer matrix. In some of the examples, media milling of the commercial dry pigments was necessary to reduce the pigment particle size and thereby enable dispersion and eventual coating with the in situ polymerized monomer. None of the examples described the preparation or use of nanosized particles of organic pigments as a raw material.
In J. App. Polym. Sci. 2008, 108, 1288 by Widiyandari et al., is described the preparation of micron-sized, spherical composite particles of pigments and polymers for use in printing inks and toners. In the article is described the use of nanosized phthalocyanine pigment particles that are core-shell particles comprised of silica in the nanoparticle core, and Pigment Blue 15:3 in the shell. The composite polymer/pigment particles are prepared by suspension-polymerization of monomers in the presence of dispersed pigment particles, thereby producing spherical micron-size composite particles ranging in particle diameter of about 4.4 to 7.4 microns. There is no description of the process for making the nanosized particles of Pigment Blue 15:3 in this article.
U.S. Patent Application Publication No. 2008/0119601 A1 discloses nanoparticle-modified polyisocyanate compositions, a process for their preparation, and their use in coating and adhesive compositions. The compositions are prepared by chemically reacting polyisocyanate compounds with an alkoxysilane (a silica precursor agent) and subsequently incorporating by dispersion the resultant inorganic nanoparticles such as silica, which are optionally surface-modified and have average particle diameters of less than 200 nm. The patent application is limited to only inorganic nanoparticles, which are modified via chemical bonding with the reactive groups of the polyisocyanate compound.
Hideki Maeta et al., “New Synthetic Method of Organic Pigment Nano Particle by Micro Reactor System,” in an abstract available on the internet at URL address: http://aiche.confex.com/aiche/s06/preliminaryprogam/abstract—40072.htm, which describes a new synthetic method of an organic pigment nanoparticle was realized by micro reactor. A flowing solution of an organic pigment, which dissolved in an alkaline aqueous organic solvent, mixed with a precipitation medium in a micro channel. Two types of micro reactor can be applied efficiently on this build-up procedure without blockage of the channel. The clear dispersion was extremely stable and had narrow size distribution, which were the features, difficult to realize by the conventional pulverizing method (breakdown procedure). These results proved the effectiveness of this process on micro reactor system.
U.S. Patent Application Publication No. 2005/0109240 describes a method of producing a fine particle of an organic pigment, containing the steps of: flowing a solution of an organic pigment dissolved in an alkaline or acidic aqueous medium, through a channel which provides a laminar flow; and changing a pH of the solution in the course of the laminar flow.
WO 2006/132443 A1 describes a method of producing organic pigment fine particles by allowing two or more solutions, at least one of which is an organic pigment solution in which an organic pigment is dissolved, to flow through a microchannel, the organic pigment solution flows through the microchannel in a non-laminar state. Accordingly, the contact area of solutions per unit time can be increased and the length of diffusion mixing can be shortened, and thus instantaneous mixing of solutions becomes possible. As a result, nanometer-scale monodisperse organic pigment fine particles can be produced in a stable manner.
K. Balakrishnan et al., “Effect of Side-Chain Substituents on Self-Assembly of Perylene Diimide Molecules: Morphology Control,” J. Am. Chem. Soc., vol. 128, p. 7390-98 (2006) describes the use of covalently-linked aliphatic side-chain substituents that were functionalized onto perylene diimide molecules so as to modulate the self-assembly of molecules and generate distinct nanoparticle morphologies (nano-belts to nano-spheres), which in turn impacted the electronic properties of the material. The side-chain substituents studied were linear dodecyl chain, and a long branched nonyldecyl chain, the latter substituent leading to the more compact, spherical nanoparticle.
U.S. Patent Application Publication No. 2006/0063873 discloses a process for preparing nano water paint comprising the steps of: A. modifying the chemical property on the surface of nano particles by hydroxylation for forming hydroxyl groups at high density on the surface of the nano particles; B. forming self-assembly monolayers of low surface energy compounds on the nano particles by substituting the self-assembly monolayers for the hydroxyl groups on the nano particles for disintegrating the clusters of nano particles and for forming the self-assembly monolayers homogeneously on the surface of the nano particles; and C. blending or mixing the nano particles having self-assembly monolayers formed thereon with organic paint to form nano water paint.
WO 2006/005536 discloses a method for producing nanoparticles, in particular, pigment particles. Said method consists of the following steps: (i) a raw substance is passed into the gas phase, (ii) particles are produced by cooling or reacting the gaseous raw substance and (iii) an electrical charge is applied to the particles during the production of the particles in step (ii), in a device for producing nanoparticles. The disclosure further relates to a device for producing nanoparticles, comprising a supply line, which is used to transport the gas flow into the device, a particle producing and charging area in order to produce and charge nanoparticles at essentially the same time, and an evacuation line which is used to transport the charged nanoparticles from the particle producing and charging area.
U.S. Pat. No. 5,679,138 discloses a process for making inkjet inks, comprising the steps of: (A) providing an organic pigment dispersion containing a pigment, a carrier for the pigment and a dispersant; (B) mixing the pigment dispersion with rigid milling media having an average particle size less than 100 μm; (C) introducing the mixture of step (B) into a high speed mill; (D) milling the mixture from step (C) until a pigment particle size distribution is obtained wherein 90% by weight of the pigment particles have a size less than 100 nanometers (nm); (E) separating the milling media from the mixture milled in step (D); and (F) diluting the mixture from step (E) to obtain an ink jet ink having a pigment concentration suitable for ink jet printers.
U.S. Patent Application Publication No. 2007/0012221 describes a method of producing an organic pigment dispersion liquid, which has the steps of: providing an alkaline or acidic solution with an organic pigment dissolved therein and an aqueous medium, wherein a polymerizable compound is contained in at least one of the organic pigment solution and the aqueous medium; mixing the organic pigment solution and the aqueous medium; and thereby forming the pigment as fine particles; then polymerizing the polymerizable compound to form a polymer immobile from the pigment fine particles.
The appropriate components and process aspects of each of the foregoing may be selected for the present disclosure in embodiments thereof, and the entire disclosure of the above-mentioned references are totally incorporated herein by reference.